DISCOVERY OF GeV γ-RAY EMISSION FROM PSR B1259–63/LS 2883

Abstract

The binary system PSR B1259-63/LS 2883 consists of a 47.8 ms radio pulsar\nthat orbits the companion Be star with a period of 3.4 years in a highly\neccentric orbit. The system is well sampled in radio, X-rays, and TeV\ngamma-rays, and shows orbital-phase-dependent variability in all observed\nfrequencies. Here we report on the discovery of >100 MeV gamma-rays from PSR\nB1259-63/LS 2883 through the 2010 pariastron passage. Using data collected with\nthe Large Area Telescope aboard Fermi from 33 days before pariastron to 75 days\nafter pariastron, PSR B1259-63/LS 2883 is detected at a significance of 13.6\nstandard deviations. The gamma-ray light curve is highly variable over the\nabove period, with changing photon index that correlates with gamma-ray flux.\nIn particular, two major flares that occur after the pariastron passage were\nobserved. The onset of gamma-ray emission occurs close to, but not at the same\norbital phases as, the two disk passages that occur ~1 month before and ~1\nmonth after the pariastron passage. The fact that the GeV orbital light curve\nis different from that of the X-ray and TeV light curves strongly suggests that\nGeV gamma-ray emission originates from a different component. We speculate that\nthe observed GeV flares may be resulting from Doppler boosting effects.\n